1. Field of the Invention
The invention relates to a process for producing crosslinkable organopolysiloxane compositions, in particular organopolysiloxane compositions which can be crosslinked at room temperature, in which the organopolysiloxane compositions are stored in an intermediate vessel before being packed in moisture-proof containers.
2. Background Art
One-component organopolysiloxane compositions which can be stored with exclusion of moisture and crosslinked at room temperature on exposure to moisture, known as RTV1 sealing compositions, have been known for a long time. Various processes for producing firm RTV1 sealing compositions have been described. Owing to a high productivity, continuous processes are preferred.
Thus, for example, according to EP-B-234 226, part of the constituents are combined in a continuously operating closed mixer in a first step. In a second step, further constituents are introduced in a reciprocating kneader. The composition is at the same time homogenized and degassed in this kneader and is subsequently packed in drums, tubes and cartridges.
EP-B-512 730 describes a process in which a screw extruder having various mixing zones is used. After compounding is complete, the RTV1 sealing composition is dispensed into containers such as cartridges or drums.
The use of a mixing apparatus having a rotating disk is disclosed in EP-B-739 652. After mixing of the constituents, water which is still present and volatile substances are removed downstream in a vacuum apparatus. The compositions are subsequently packed in aluminum cartridges.
EP-A-1 008 613 describes the use of a mixing turbine which has axial flow and in which all constituents of the mixture are mixed in one step. After degassing, the finished mixture is dispensed into hobbocks, drums, large containers or cartridges.
The known continuously operating processes provide constant amounts of RTV1 sealing compositions per unit time, and are operational over a long period of time. At the end of the respective continuous processes, the sealing compositions are packed in moisture-proof containers. In general, the compositions are firstly dispensed into drums or open vessels such as buckets. The RTV1 sealing compositions are subsequently packed in ready-to-use moisture-proof containers such as tubes, cartridges or bags either immediately or after relatively long transport time. These packing processes are usually associated with considerable problems since the highly viscous RTV1 sealing compositions are firm and sensitive to hydrolysis.
Since continuously operating plants having a comparatively low throughput of a few hundred of kilograms per hour are also economically feasible, there are frequently very long dispensing times for dispensing into relatively large, open intermediate vessels such as buckets or drums. During this time, the RTV1 sealing compositions are not sufficiently protected against the action of moisture. Engineering measures such as blanketing the dispensing unit with dry air can often achieve only a partial and an unsatisfactory reduction in entry of moisture.
Furthermore, the use of particular apparatuses in the continuous production of liquids which even out fluctuations between quantities of product produced and processed is also known. In principle, the installation of such buffer vessels is only advantageous in the case of production processes which are subject to malfunctions and have large fluctuations in the amount produced. Such an apparatus for equalizing the stream of spontaneously flowing liquids between continuous production and downstream processing plants which operate essentially continuously is described, for example, in DE-A-100 20 571.
In addition, in order to avoid disadvantageous overcapacities in the long term it is necessary to carefully match the continuous production and the continuous consumption of amounts of product per unit time. The amount of product which has to be made available per unit time when the buffer vessel is emptied therefore corresponds exactly to the amount of product which is continuously obtained from the continuous production plant. This means that in the event of the production plant going down, the buffer vessel only has to provide the amount of product per unit time which the production plant would have produced.
However, in processes for dispensing RTV1 sealing compositions it is necessary for a large amount of product to be conveyed discontinuously in short time intervals. Single buffer vessels are thus not suitable for quickly dispensing large amounts of product.